The present invention relates generally to improvements in phase-jump detector-corrects, and more particularly pertains to new and improved phase-jump detector-correctors for use with phase modulation schemes such as modified eight phase or two level eight phase modulation wherein the phase vectors are relatively displaced at N.sup.o and symmetrically disposed about the X, Y coordinates of the phase plane.
Sudden phase changes occurring on telephone voice channels are quite common. These phase changes can be caused by switching of carrier supplies not in phase, or the substitution of a broadband facility having a different propagation time. The effect in the voice channel is the creation of an equal phase change across all frequencies. Such phase changes are usually accomplished by amplitude transients during the recovery of steady state in the voide-band channel. Upon recovery, however, the phase change generated across all the frequencies remains.
Modems utilized on these voice channels usually provide equalization circuits that compensate for such phase-jumps. In the instance where modulation schemes that provide for vector symbol symmetry above the X--Y phase plane axes are used with vector spacings of 45.degree., a phase-jump of 45.degree. becomes very difficult to detect. Without detecting and correcting for such a phase-jump, the equalizer operating in the voice-band modem would no longer be able to correct for the amplitude and phase distortion inherent in the voice-band channel, thereby generating decoding errors. As a result, the equalizer would have to be shut down and the line reequalized as if at start up.